The temperature dependence of the thermodynamic potential of quantum chromodynamics (QCD), the specific heat, and the quark effective mass are calculated for imbalanced quark matter in the limit of a large number of quark flavors (large-$N_F$), which corresponds to the random phase approximation. Also a generalization of the relativistic Landau effective-mass relation in the imbalanced case is given, which is then applied to this thermodynamic potential.